Many types and sizes of storage tanks are widely used by industrial and manufacturing enterprises to hold chemicals, fuels and other commercial products. There are above-ground and underground tanks, and various regulations put in place by national and state-level environmental agencies apply to storage tanks. In regard to above-ground storage tanks, when located outdoors in warmer climates, they may absorb substantial amounts of solar radiation. Tanks may also be located on rail cars and trucks and form the major portion of tanker ships. All such storage tanks may suffer from the heating effects of solar radiation.
When tanks are located in full sunlight, as they often must be, and the sun's heat causes them to reach certain temperatures, the surface temperature of the stored substance also becomes warmer and some of the product being stored can evaporate or “vaporize”. The longer the sun strikes the tank, the more it heats not only the tank's exterior, but also its interior contents. When vaporization occurs, air pollution results unless the vapors are captured and sent to a control device. Seals of different types have been designed for floating roof storage tanks to help minimize evaporative losses. Various vapor recovery and treatment systems have been developed in order to reduce the amount of volatile organic compound (VOC) releases to the atmosphere as well as treatment measures for the releases of other types of pollutants such as nitrogen oxides (NOx).
Many of the currently available technologies for pollution control are complex, expensive and may also involve the release of certain pollutants in the course of their operation. The present invention provides a prevention-based, cost-effective solution that releases no emissions of its own and is projected to be helpful in reducing VOC emissions of certain types of stored substances from various types and sizes of tanks. The types of tanks may include fixed roof tanks, external floating roof tanks, internal floating roof tanks, domed roof tanks, as well as storage tanks for propane and LPG that may be cylindrical, “bullet” tanks and spherical tanks. Drawings and descriptions of some commonly used tank types and seals can be found in a chapter on Liquid Storage Tanks at http://www.epa.gov/ttn/cheif/ap42/ch07/final/c07s01.pdf, accessed Mar. 20, 2003.
Toxic emissions may be discharged from such petrochemical storage tanks when increased levels of solar radiation and ambient air temperature induce substantial heating of the tanks and their contents. Keeping an inventory of toxic emission releases to the environment, and working to reduce such toxic releases, has brought about significant improvements in environmental quality over the years. In a U.S. Environmental Protection Agency (EPA) document entitled “Taking Toxics Out of the Air” at http://www.epa.gov/oar/oaqps/takingtoxics/sum4.html, (accessed Jan. 16, 2003), various measures and rules are discussed that are intended to reduce toxic emissions. One section, “Oil and Natural Gas Production and Natural Gas Transmission and Storage” relates that “Emissions of air toxics from oil and natural gas production and natural gas transmission and storage occur during separation, upgrade, transport, and storage of crude oil, condensate, natural gas, and related products.” Releases from oil and natural gas facilities, the report continues, may include benzene (a known human carcinogen) and other VOCs that are “suspected to cause cancer or other serious health effects”.
From the same report, VOCs' role in ground level ozone (smog) creation is discussed briefly, and the EPA announced the expected benefits to air quality projected to result from the rule changes. Those rules required “controls for the following emission points at oil and natural gas production facilities: process vents at some glycol dehydration units, tanks with flashing emission potential, and some fugitive emission sources. Natural gas transmission and storage facilities will be required to control emissions from process vents at some glycol dehydration units.”
EPA gathers and maintains information on toxic releases by industrial sources in each state; such information regarding releases, both on-site and off-site to the air, land and water, are available for various years at http://www.epa.gov/tri/tridata, accessed Mar. 20, 2003. It is therefore of high importance to strive to limit or eliminate releases to the environment of substances that may be harmful to humans and wildlife. Pollution control technologies are developed and brought to market so they may play a key role in this effort. The shade panel assembly of the present invention can be instrumental in air quality improvement, not only at a particular industrial plant, but also across a wide area through which it has been put into use. This is due to its VOC-reduction potential which, in turn, will help lower the amount of ground-level ozone formation thereby providing public health benefits during the summer months (the “ozone season”) and economic benefits for the company whose stored product (that previously has been lost through vaporization) is not lost to the atmosphere but can be used or sold instead.
The primary cause of this temperature related vaporization loss is the presence or absence of direct sunlight. The longer the sun strikes the tank, the more it heats not only the tank but also its contents such as oil, gasoline and a host of other chemicals. As the temperature of the exterior surfaces or “skin temperature” of the tank increases, it causes the liquids within the tank to expand and evaporate, converting some of the liquid to vapor form. If this expansion is drastic enough, it will cause the tank to release some of the vapors into the atmosphere to prevent the tank from over-pressurizing and rupturing. This not only causes air pollution but also wastes natural resources as stated above, vaporization reduces the amount of product that can be sold, thereby reducing profits. On large tank farms, and in the warmest areas of the country/world, this loss of product and resulting pollution caused by temperature fluctuations over an extended period of time is quite substantial.
Accordingly, the need exists for new technologies to prevent heating of storage tanks or reduce VOC emissions from those tanks.